Hw2-Answer

Hw2-Answer

2.1 Define the following terms: data model, database schema, database state, internal schema, conceptual schema, external schema, data independence, DDL, DML, SDL, VDL, query language, host language, data sublanguage, database utility, catalog, client/server architecture, three-tier architecture, and n-tier architecture.
Answer:
data model: a collection of concepts that can be used to describe the structure of a database-provides the necessary means to achieve this abstraction.
database schema: The description of a database is called the database schema, which is specified during database design and is’nt expected to change frequently.
database state: The data in the database at a particular moment in time is called a database state or snapshot. It’s also called the current set of occurrences or instances in the database.
internal schema: describe the physical storage structure of the database. The internal schema uses a physical data model and describe the complete details of data storage and access paths for the database.
conceptual schema: The conceptual schema hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints.
external schema: Each external schema describes the part of the database that a particular user group is interested in and hides the rest of the database from that user group.
data independence: It can be defined as the capacity to change the schema at one level of a database system without having to change the schema at the next higher level.
DDL: It is used by the DBA and by database designer to define both schema.
DML: The DBMS provides a set of operations or a language called the data manipulation language for typical manipulations include retrieval, insertion, deletion, and modification of the data.
SDL: It is used to specify the internal schema.
VDL: It is used to specify user views and their mappings to the conceptual schema.
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